Lubricating oil compositions for internal combustion engines generally contain a variety of additives to reduce or control deposits, wear, corrosion, etc. The present invention is concerned with compositions useful as dispersants in lubricating oil compositions.
In lubricating oils, dispersants function to control sludge, carbon, and varnish produced primarily by the incomplete combustion of the fuel, or impurities in the fuel, or impurities in the base oil used in the lubricating oil composition. Dispersants also control viscosity increase due to the presence of soot in diesel engine lubricating oils.
One of the most effective classes of lubricating oil dispersants is polyalkylene succinimides. In some cases, the succinimides have also been found to provide fluid-modifying properties, or a so-called viscosity index credit, in lubricating oil compositions. It produces a reduction in the amount of viscosity index improver that would otherwise have to be used.
Polyalkylene succinimides are generally prepared by the reaction of the corresponding polyalkylene succinic anhydride with a polyalkyl polyamine. Polyalkylene succinic anhydrides are generally prepared by a number of well-known processes. For example, there is a well-known thermal process (see, e.g., U.S. Pat. No. 3,361,673), an equally well-known chlorination process (see, e.g., U.S. Pat. No. 3,172,892), a combination of the thermal and chlorination processes (see, e.g., U.S. Pat. No. 3,912,764), and free radical processes (see, e.g., U.S. Pat. Nos. 5,286,799 and 5,319,030). Such compositions include one-to-one monomeric adducts (see, e.g., U.S. Pat. Nos. 3,219,666 and 3,381,022), as well as "multiply adducted" products, adducts having alkenyl-derived substituents adducted with at least 1.3 succinic groups per alkenyl-derived substituent (see, e.g., U.S. Pat. No. 4,234,435).
U.S. Pat. Nos. 3,361,673 and 3,018,250 describe the reaction of an alkenyl- or alkyl-substituted succinic anhydride with a polyamine to form alkenyl or alkyl succinimide lubricating oil dispersants and/or detergent additives.
U.S. Pat. No. 4,612,132 teaches that alkenyl or alkyl succinimides may be modified by reaction with a cyclic or linear carbonate or chloroformate such that one or more of the nitrogens of the polyamine moiety is substituted with a hydrocarbyl oxycarbonyl, a hydroxyhydrocarbyl oxycarbonyl, or a hydroxy poly(oxyalkylene) oxycarbonyl. These modified succinimides are described as exhibiting improved dispersancy and/or detergency in lubricating oils.
U.S. Pat. No. 4,747,965 discloses modified succinimides similar to those disclosed in U.S. Pat. No.4,612,132, except that the modified succinimides are described as being derived from succinimides having an average of greater than 1.0 succinic groups per long chain alkenyl substituent.
U.S. Pat. No. 4,234,435 teaches a polyalkene-derived substituent group with a number average molecular weight (M.sub.n) in the range of 1500 to 3200. For polybutenes, an especially preferred M.sub.n range is 1700 to 2400.
U.S. Pat. No. 5,112,507 discloses a polymeric ladder type polymeric succinimide dispersant in which each side of the ladder is a long chain alkyl or alkenyl, generally having at least about 30 carbon atoms, preferably at least about 50 carbon atoms. The dispersant is described as having improved hydrolytic stability and shear stress stability, produced by the reaction of certain maleic anhydride-olefin copolymers with certain polyamines. The patent further teaches that the polymer may be post-treated with a variety of post-treatments, and describes procedures for post-treating the polymer with cyclic carbonates, linear mono- or polycarbonates.
U.S. Pat. Nos. 5,334,321 and 5,356,552 disclose certain cyclic carbonate post-treated alkenyl or alkylsuccinimides having improved fluorocarbon elastomer compatibility, which are preferably prepared by the reaction of the corresponding substituted succinic anhydride with a polyamine having at least four nitrogen atoms per mole.
U.S. Pat. No. 5,716,912 discloses polyalkylene succinimides prepared by reacting, under reactive conditions, a mixture of a polybutene succinic acid derivative, an unsaturated acidic reagent copolymer of an unsaturated acidic reagent and an olefin, and a polyamine, then treating those succinimides with cyclic carbonates, linear mono- or polycarbonates or a boron compound.